ABSTRACT
Sodium bicarbonate (NaHCO3)-extractable phosphorus, commonly termed Olsen-P (Olsen
et al. 1954), has a long history of worldwide use as an index of soil-available P on which to
base P fertilizer recommendations (Cox 1994). It has been successfully used as a soil test for
P in both acid and calcareous soils (Kamprath and Watson 1980). As a soil test, Olsen-P is
sensitive to management practices that influence bioavailable soil P levels, such as fertilizer
(O’Halloran et al. 1985) or manure (Qian et al. 2004) additions, although it is not suitable for
P extraction from soils amended with relatively water-insoluble P materials such as rock
phosphate (Mackay et al. 1984; Menon et al. 1989).
